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          <span data-v-64685f0e>2020 - </span>
          2021
        </a></span></div></div> <div data-v-2d5f533b><main class="page"><div class="page-title" style="display:none;"><h1 class="title">第三章 语言基础</h1> <div data-v-3b7f5bdf><i class="iconfont reco-account" data-v-3b7f5bdf><span data-v-3b7f5bdf>伊水河</span></i> <i class="iconfont reco-date" data-v-3b7f5bdf><span data-v-3b7f5bdf>2020-10-26 11:20:20</span></i> <i class="iconfont reco-eye" data-v-3b7f5bdf><span id="/note/professionalJavascript4/3.html" data-flag-title="Your Article Title" class="leancloud-visitors" data-v-3b7f5bdf><a class="leancloud-visitors-count" style="font-size:.9rem;font-weight:normal;color:#999;"></a></span></i> <i class="iconfont reco-tag tags" data-v-3b7f5bdf><span class="tag-item" data-v-3b7f5bdf>javascript高级程序设计</span></i></div></div> <div class="theme-reco-content content__default" style="display:none;"><h2 id="and"><a href="#and" class="header-anchor">#</a> ++ and --</h2> <h3 id="前缀"><a href="#前缀" class="header-anchor">#</a> 前缀</h3> <div class="language-javascript extra-class"><pre class="language-javascript"><code><span class="token keyword">let</span> num1<span class="token operator">=</span><span class="token number">2</span>
<span class="token keyword">let</span> num2<span class="token operator">=</span><span class="token number">20</span>
<span class="token keyword">let</span> num3<span class="token operator">=</span><span class="token operator">--</span>num1<span class="token operator">+</span>num2
<span class="token keyword">let</span> num4<span class="token operator">=</span>num1<span class="token operator">+</span>num2

console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num3<span class="token punctuation">)</span><span class="token comment">//21</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num4<span class="token punctuation">)</span><span class="token comment">//21</span>
</code></pre></div><p><code>num3</code>等于21是因为<code>num1</code>先减1，后加<code>num2</code>。<code>num4</code>也是21，是因为<code>num1</code>已经被<code>--</code>过了，值已经递减。</p> <h3 id="后缀"><a href="#后缀" class="header-anchor">#</a> 后缀</h3> <div class="language-javascript extra-class"><pre class="language-javascript"><code><span class="token keyword">let</span> num1<span class="token operator">=</span><span class="token number">2</span>
<span class="token keyword">let</span> num2<span class="token operator">=</span><span class="token number">20</span>
<span class="token keyword">let</span> num3<span class="token operator">=</span>num1<span class="token operator">--</span><span class="token operator">+</span>num2
<span class="token keyword">let</span> num4<span class="token operator">=</span>num1<span class="token operator">+</span>num2

console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num3<span class="token punctuation">)</span><span class="token comment">//22</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num4<span class="token punctuation">)</span><span class="token comment">//21</span>
</code></pre></div><p>这里的不同之处在于，计算<code>num3</code>时使用的是<code>num1</code>的原始值（2），计算<code>num4</code>则和上面一样，是已经<code>--</code>的值了。</p> <ul><li><code>自备</code>：运算符优先级：前缀&gt;一般&gt;后缀</li></ul> <p>参见：<a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table" target="_blank" rel="noopener noreferrer">运算符优先级<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></p> <table class="fullwidth-table"><tbody><tr><th>优先级</th> <th>运算类型</th> <th>关联性</th> <th>运算符</th></tr> <tr><td>21</td> <td><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Grouping" target="blank">圆括号</a></td> <td>n/a（不相关）</td> <td><code>( … )</code></td></tr> <tr><td rowspan="5">20</td> <td><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Property_Accessors#点符号表示法" target="blank">成员访问</a></td> <td>从左到右</td> <td><code>… . …</code></td></tr> <tr><td><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Property_Accessors#括号表示法" target="blank">需计算的成员访问</a></td> <td>从左到右</td> <td><code>… [ … ]</code></td></tr> <tr><td><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/new" target="blank">new</a> (带参数列表)</td> <td>n/a</td> <td><code>new … ( … )</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Guide/Functions" target="blank">函数调用</a></td> <td>从左到右</td> <td><code>… ( <var>… </var>)</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Optional_chaining" target="blank">可选链（Optional chaining）</a></td> <td>从左到右</td> <td><code>?.</code></td></tr> <tr><td rowspan="1">19</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/new" target="blank">new</a> (无参数列表)</td> <td>从右到左</td> <td><code>new …</code></td></tr> <tr><td rowspan="2">18</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Increment" target="blank">后置递增</a>(运算符在后)</td> <td colspan="1" rowspan="2">n/a<br>
     </td> <td><code>… ++</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Decrement" target="blank">后置递减</a>(运算符在后)</td> <td><code>… --</code></td></tr> <tr><td colspan="1" rowspan="10">17</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Logical_Operators#Logical_NOT" target="blank">逻辑非</a></td> <td colspan="1" rowspan="10">从右到左</td> <td><code>! …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_NOT" target="blank">按位非</a></td> <td><code>~ …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Unary_plus" target="blank">一元加法</a></td> <td><code>+ …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Unary_negation" target="blank">一元减法</a></td> <td><code>- …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Increment" target="blank">前置递增</a></td> <td><code>++ …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Decrement" target="blank">前置递减</a></td> <td><code>-- …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/typeof" target="blank">typeof</a></td> <td><code>typeof …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/void" target="blank">void</a></td> <td><code>void …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/delete" target="blank">delete</a></td> <td><code>delete …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await" target="blank">await</a></td> <td><code>await …</code></td></tr> <tr><td>16</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Exponentiation" target="blank">幂</a></td> <td>从右到左</td> <td><code>… ** …</code></td></tr> <tr><td rowspan="3">15</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Multiplication" target="blank">乘法</a></td> <td colspan="1" rowspan="3">从左到右<br>
     </td> <td><code>… * …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Division" target="blank">除法</a></td> <td><code>… / …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Remainder" target="blank">取模</a></td> <td><code>… % …</code></td></tr> <tr><td rowspan="2">14</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Addition" target="blank">加法</a></td> <td colspan="1" rowspan="2">从左到右<br>
     </td> <td><code>… + …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Subtraction" target="blank">减法</a></td> <td><code>… - …</code></td></tr> <tr><td rowspan="3">13</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators" target="blank">按位左移</a></td> <td colspan="1" rowspan="3">从左到右</td> <td><code>… &lt;&lt; …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators" target="blank">按位右移</a></td> <td><code>… &gt;&gt; …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators" target="blank">无符号右移</a></td> <td><code>… &gt;&gt;&gt; …</code></td></tr> <tr><td rowspan="6">12</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Less_than_operator" target="blank">小于</a></td> <td colspan="1" rowspan="6">从左到右</td> <td><code>… &lt; …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Less_than__or_equal_operator" target="blank">小于等于</a></td> <td><code>… &lt;= …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Greater_than_operator" target="blank">大于</a></td> <td><code>… &gt; …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Greater_than_or_equal_operator" target="blank">大于等于</a></td> <td><code>… &gt;= …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/in" target="blank">in</a></td> <td><code>… in …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/instanceof" target="blank">instanceof</a></td> <td><code>… instanceof …</code></td></tr> <tr><td rowspan="4">11</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Equality" target="blank">等号</a></td> <td colspan="1" rowspan="4">从左到右<br>
     </td> <td><code>… == …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Inequality" target="blank">非等号</a></td> <td><code>… != …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Identity" target="blank">全等号</a></td> <td><code>… === …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Nonidentity" target="blank">非全等号</a></td> <td><code>… !== …</code></td></tr> <tr><td>10</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_AND" target="blank">按位与</a></td> <td>从左到右</td> <td><code>… &amp; …</code></td></tr> <tr><td>9</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_XOR" target="blank">按位异或</a></td> <td>从左到右</td> <td><code>… ^ …</code></td></tr> <tr><td>8</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_OR" target="blank">按位或</a></td> <td>从左到右</td> <td><code>… | …</code></td></tr> <tr><td>7</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Logical_Operators#Logical_AND" target="blank">逻辑与</a></td> <td>从左到右</td> <td><code>… &amp;&amp; …</code></td></tr> <tr><td>6</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Logical_Operators#Logical_OR" target="blank">逻辑或</a></td> <td>从左到右</td> <td><code>… || …</code></td></tr> <tr><td>5</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator" target="blank">空值合并</a></td> <td>从左到右</td> <td><code>… ?? …</code></td></tr> <tr><td>4</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Conditional_Operator" target="blank">条件运算符</a></td> <td>从右到左</td> <td><code>… ? … : …</code></td></tr> <tr><td rowspan="16">3</td> <td rowspan="16"><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Assignment_Operators" target="blank">赋值</a></td> <td rowspan="16">从右到左</td> <td><code>… = …</code></td></tr> <tr><td><code>… += …</code></td></tr> <tr><td><code>… -= …</code></td></tr> <tr><td><code>… **= …</code></td></tr> <tr><td><code>… *= …</code></td></tr> <tr><td><code>… /= …</code></td></tr> <tr><td><code>… %= …</code></td></tr> <tr><td><code>… &lt;&lt;= …</code></td></tr> <tr><td><code>… &gt;&gt;= …</code></td></tr> <tr><td><code>… &gt;&gt;&gt;= …</code></td></tr> <tr><td><code>… &amp;= …</code></td></tr> <tr><td><code>… ^= …</code></td></tr> <tr><td><code>… |= …</code></td></tr> <tr><td><code>… &amp;&amp;= …</code></td></tr> <tr><td><code>… ||= …</code></td></tr> <tr><td><code>… ??= …</code></td></tr> <tr><td colspan="1" rowspan="2">2</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/yield" target="blank">yield</a></td> <td colspan="1" rowspan="2">从右到左</td> <td><code>yield …</code></td></tr> <tr><td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/yield*" target="blank">yield*</a></td> <td><code>yield* …</code></td></tr> <tr><td>1</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Spread_operator" target="blank">展开运算符</a></td> <td>n/a</td> <td><code>...</code> …</td></tr> <tr><td>0</td> <td><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/Comma_Operator" target="blank">逗号</a></td> <td>从左到右</td> <td><code>… , …</code></td></tr></tbody></table></div> <footer class="page-edit" style="display:none;"><!----> <!----></footer> <!----> <!----> <!----></main> <!----></div></div></div></div><div class="global-ui"><div class="back-to-ceiling" style="right:1rem;bottom:6rem;width:2.5rem;height:2.5rem;border-radius:.25rem;line-height:2.5rem;display:none;" data-v-c6073ba8 data-v-c6073ba8><svg t="1574745035067" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5404" class="icon" data-v-c6073ba8><path d="M526.60727968 10.90185116a27.675 27.675 0 0 0-29.21455937 0c-131.36607665 82.28402758-218.69155461 228.01873535-218.69155402 394.07834331a462.20625001 462.20625001 0 0 0 5.36959153 69.94390903c1.00431239 6.55289093-0.34802892 13.13561351-3.76865779 18.80351572-32.63518765 54.11355614-51.75690182 118.55860487-51.7569018 187.94566865a371.06718723 371.06718723 0 0 0 11.50484808 91.98906777c6.53300375 25.50556257 41.68394495 28.14064038 52.69160883 4.22606766 17.37162448-37.73630017 42.14135425-72.50938081 72.80769204-103.21549295 2.18761121 3.04276886 4.15646224 6.24463696 6.40373557 9.22774369a1871.4375 1871.4375 0 0 0 140.04691725 5.34970492 1866.36093723 1866.36093723 0 0 0 140.04691723-5.34970492c2.24727335-2.98310674 4.21612437-6.18497483 6.3937923-9.2178004 30.66633723 30.70611158 55.4360664 65.4791928 72.80769147 103.21549355 11.00766384 23.91457269 46.15860503 21.27949489 52.69160879-4.22606768a371.15156223 371.15156223 0 0 0 11.514792-91.99901164c0-69.36717486-19.13165746-133.82216804-51.75690182-187.92578088-3.42062944-5.66790279-4.76302748-12.26056868-3.76865837-18.80351632a462.20625001 462.20625001 0 0 0 5.36959269-69.943909c-0.00994388-166.08943902-87.32547796-311.81420293-218.6915546-394.09823051zM605.93803103 357.87693858a93.93749974 93.93749974 0 1 1-187.89594924 6.1e-7 93.93749974 93.93749974 0 0 1 187.89594924-6.1e-7z" p-id="5405" data-v-c6073ba8></path><path d="M429.50777625 765.63860547C429.50777625 803.39355007 466.44236686 1000.39046097 512.00932183 1000.39046097c45.56695499 0 82.4922232-197.00623328 82.5015456-234.7518555 0-37.75494459-36.9345906-68.35043303-82.4922232-68.34111062-45.57627738-0.00932239-82.52019037 30.59548842-82.51086798 68.34111062z" p-id="5406" data-v-c6073ba8></path></svg></div><APlayer audio="" fixed="true" theme="#b7daff" loop="loop" order="random" preload="auto" volume="0.7" mutex="true" lrc-type="3" list-folded="true" list-max-height="250" storage-name="vuepress-plugin-meting" id="aplayer-fixed"></APlayer></div></div>
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